Smelting of metal ores generates smelter by-products such as flue dusts and sludges that typically contain substantial amounts of environmentally hazardous substances such as sulfur, arsenic, and heavy metals. Hence, flue dusts and sludges are regarded by the United States Environmental Protection Agency (EPA) as hazardous materials requiring safe methods for disposal. This is because the hazardous substances in flue dusts and sludges can leach therefrom by rain and other natural waters and may contaminate groundwater.
Unfortunately, known disposal processes adaptable to smelter flue dusts and sludges are expensive. Also, the only disposal method for copper-smelter flue dust currently acceptable to the EPA comprises recycling the dust to the smelter, which can be prohibitively deleterious to the quality of copper produced by the smelter. Furthermore, known disposal processes that allow recovery of valuable metals from flue dust and smelter sludges entail capital and operating costs that exceed the revenue obtainable from the recovered metal. As a result, some smelter operators currently stockpile flue dust and sludge in anticipation that more economical disposal methods will be developed. Other smelter operators forego resource recovery entirely in favor of storage of the dust or sludge in licensed hazardous waste sites. Costs of these disposal methods are prohibitively high for many smelter operators.
Hence, there is a need for methods for treating smelter flue dusts and sludges that permit recovery of valuable metal therefrom while converting other hazardous constituents thereof into non-leachable compounds.
There is also a need for such methods that permit environmentally safe disposal of smelter flue dust and sludge, thereby eliminating the need to stockpile or encapsulate the flue dust or sludge.
There is also a need for such methods that do not produce toxic or hazardous by-products.
There is also a need for such methods that are low-cost.